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# MIXPRE

MIXPRE = 0 | 1 | 2 | 3
Default: MIXPRE = 1

Description: MIXPRE specifies the metric in the Broyden mixing scheme(IMIX=4).

• MIXPRE=0
No preconditioning, metric=1
• MIXPRE=1
"Inverse Kerker" metric with automatically determined BMIX (determined in such a way that the variation of the preconditioning weights covers a range of a factor 20)
• MIXPRE=2
"Inverse Kerker" metric with automatically determined BMIX (determined in such a way that the variation of the preconditioning weights covers a range of a factor 200)
• MIXPRE=3 (implemented for test purposes; not recommended)
"Inverse Kerker" metric with BMIX from INCAR, the weights for the metric are given by
${\displaystyle P\left(G\right)=1+{\frac {B^{2}}{G^{2}}}}$
with ${\displaystyle B}$ =BMIX.

The preconditioning is done only on the total charge density (i.e. up+down component) and not on the magnetization charge density (i.e. up-down component). Up to now we have found that introduction of a metric always improves the convergence speed. The best choice is MIXPRE=1 (i.e. the default).